The present invention relates to a new and improved construction of apparatus for the localization of a fault on a line wherein there is formed from at least one measurement voltage signal derived from a line voltage and at least one measurement current signal derived from a line current an evaluation signal characterizing the direction and/or distance of a fault location with respect to a reference location on the line which is determinable or controlled by at least one adjustment magnitude.
The present invention is an improvement upon the apparatus disclosed in the commonly assigned, copending United States application Ser. No. 677,685, filed Apr. 16, 1976, of Otto Lanz and Michael Vitins, entitled "Process And Apparatus For Locating Faults On A Line," the disclosure of which is incorporated herein by reference.
In U.S. Pat. No. 3,590,368 there is disclosed an apparatus for localization of a fault on a line wherein at two measurement locations there is formed from the line voltage and the line current a respective traveling wave signal, i.e. a signal, the temporal progression thereof i.e. its course as a function of time corresponds to that of a traveling wave at the measurement location traveling on the line. Thus, at both measurement locations there are traveling wave signals associated with the same direction of propagation, which then are compared with one another by means of a special control line. The thus determined damping of a traveling wave moving from one measurement location to the other provides an indication regarding the presence of a fault within the line section between both measurement locations, thus renders possible fault localization. What is of disadvantage is the requirement for two measurement stations and a special control line as well as the prerequisite of sinusoidal measurment- and traveling wave signals for the damping determination. The last-mentioned prerequisite requires the suppression of the initially strong transient upper harmonics of the line voltage and the line current which follow the occurrence of a fault or the expiration of a sufficient time interval for the decay of such upper harmonics. Both of these conditions are undesired in consideration of the strived for fault localization without any time delay.
There is disclosed in the previously mentioned copending application an apparatus for locating faults which enables monitoring a line section or in fact a number of such sections for faults from a single measurement location, these line sections being bounded by reference locations on the line which are freely determinable i.e. controlled by means of regulation or adjustment magnitudes at a single measurement station. The fault direction determination with respect to two neighboring reference locations or with respect to the measurement location and the neighboring reference location already provides localization of the fault. On the other hand, especially also when selecting only one reference location, it is possible with such apparatus to carry out a fault localization by fault direction determination with respect to a reference location or also the measurement location in connection with a fault distance determination with respect to the reference location or measurement location. There is thus either necessary a twofold evaluation process with two different reference location adjustments or for the measurement location and a reference location adjustment or a distance determination in addition to a direction determination. The distance determination in cases where the fault location is at a greater distance from the reference location does place comparatively great requirements upon the precision of the circuitry if there is required the same absolute fault limits as with lesser distances, and under circumstances also requires longer integration times during the signal processing.
On the other hand, the fault direction determination with respect to a reference location for fault locations near or in the direct neighborhood of such reference location is associated with uncertainty. This is so because the course of the evaluation signal over the fault location-reference location distance, upon coincidence of the fault location and reference location, generally passes through null and thus the evaluation signal at the neighborhood of this null cross-over merges with the disturbance signal peak.
Therefore problems exist both for exceedingly closely situated faults and also for remotely located faults relative to a reference location as concerns the reliability of the direction determination and the distance accuracy.